End closure for rosette-shaped centrifuges



Oct. 19, 1965 D. A. BOYLAND 3,212,843

END CLOSURE FOR ROSETTE-SHAPED CENTRIFUGES Filed Dec. 29, 1950 .Z).fl 150 6am 4.. I a 4 United States Patent 3,212,843 END CLOSURE FOR ROSETTE-SHAPED CENTRIFUGES Donald Arthur Boyland, Kenton, England, assignor to The General Electric Company Limited, London,

England v Filed Dec. 29, 1950, Ser. No. 203,247

5 Claims. (Cl. 233-1) The present invention relates to centrifuges for operation at high peripheral velocities and comprising a hollow body of generally cylindrical shape having end plates to close its ends. The body may have an outer shell of rosette shape in cross-section, as described in the specification of United States application Serial No. 731,067 filed Feb. 26, 1947, now Patent 3,108,955 issued Oct. 29, 1963, and the outer shell may be supported from a central hub by means of radial spokes.

In such centrifuges a difficulty arises in designing an end plate and in fastening such a plate to the body in such a manner that the joint between these parts can withstand the very large stresses met with in use. As the centrifuge is run up to speed, the diameter of the body and the diameter of the end plates will both increase owing to the strain produced by the centrifugal stresses. It is diflicult to arrange that these expansions are exactly equal at all speeds since the rotor, being hollow, will expand by an amount different from that by which a plate forming a closure therefor and sufliciently substantial to support itself under the centrifugal loading to which it is exposed during rotation would expand when rotating at the same speed because the stresses are supported in different ways in the two cases. If the expansions are not equal there will be relative movements at the contact surface between the end plate and the body and thus the maintenance of a gas-tight joint at all speeds is difficult. It is the object of the present invention to provide a centrifuge rotor having an end plate in which the difliculty of maintaining a gas-tight joint is removed or largely reduced.

Broadly, according to one aspect of the invention, in a centrifuge rotor comprising a hollow body and an end plate, the end plate is formed by a flat frame which is fixed to and is designed to have the same expansion as the hollow body under the centrifugal forces generated therein by rotation of the rotor but is not by itself capable of forming a closure for the end of said body, and there is sealed to and supported by said frame a diaphragm forming a closure proper but which is so thin as to be capable of being constrained by said frame to maintain substantially the same expansion (when the rotor rotates) as said frame, the thinness of the diaphragm being such that the necessary constraint does not set up loads, in the joint between the diaphragm and the frame, large enough to change the expansion of the frame appreciably. So thin a diaphragm would not comport itself as a self-supporting body against the loading which the centrifugal forces exert on it when the centrifuge is in operation, and the diaphragm is accordingly arranged to abut against substantially the whole area of the flat face of the frame to which it is sealed, so as to provide support for the diaphragm against collapse under the centrifugal loading. The diaphragm is likely to be more highly stressed than the body when in operation and is therefore made of a material which is sufficiently ductile or elastic to withstand the changes in its dimensions. The frame may be in two like parts and the diaphragm may be fixed between these parts.

The invention will be described by way of example with reference to the accompanying drawing:

FIGURE 1 is a transverse sectional view, along the line II of FIGURE 2, of one-half of a rotor according to the invention, and

3,212,843 Patented Oct. 19, 1965 FIGURE 2 is a view in sectional elevation of a part of the rotor of FIGURE 1 along the line II-II of FIG- URE l.

The rotor comprises an outer shell 10 connected to a central hub 11 by spokes 12. The end plate comprises two like members 13 and 14 consisting of an outer rim portion 15 and spokes 16 of the same general shape as the corresponding parts of the outer shell but, as shown, they need not be of the same dimensions so long as the expansion of the members 13 and 14 under centrifugal stress is substantially the same as that of the body of the rotor. Between the frame members 13 and 14 is a diaphragm 17 which is so thin as not to affect the expansion of the frame members, but which serves to provide a fluid-tight closure.

The surface 18 of the end plate may be fastened to the surface 19 of the body, and the two frame members may be fastened on either side of the diaphragm 17, by any suitable means; for instance they may be copper-brazed, soft-soldered, or a cement such as is known as Araldite cement may be used.

It is not essential that the body and end plates should be of the same material so long as the requirements of like expansion under centrifugal stress are met. In one example the body 10, 11, frame members 13, 14 and diaphragm 17 are all of a high tensile steel such as that known as EN30. The diaphragm may however be of mild steel. No doubt many other materials will be found suitable for this purpose. It is usually arranged that when the rotor is run up to its operational speed, the body and frame members are stressed within their elastic limit and the material of the diaphragm is strained beyond its elastic limit. The materials referred to are found to operate satisfactorily under the conditions. In this example the thickness of each of the frame members is M1. inch and that of the diaphragm is 0.01 to 0.02 inch.

It is further not essential that the spokes 16 of the frame members 13, 14 should be in register with those 12 of the body. They may, for example, be staggered relatively to one another so that the spokes 16 lie between and if desired symmetrically between the median radial planes of the spokes 12.

Where it is possible the radial breadth of the shell 10 and rim 13 are preferably made the same and the two parts then of necessity have the same expansions under centrifugal stress if they are of the same material. In the example illustrated these breadths are for certain reasons required to be different and nevertheless it is found possible, so long as the difference in breadth is not excessive, to design the parts in such a manner that the same expansions are obtained. If preferred, however a lamina of the same form as the cross-section of the rotor, but having a rim of the same dimensions as the rim 15 of the frame members 13 and 14, may be fixed, for example by copper-brazing, to the end of the shell.

It is of course to be understood that the invention is applicable to shells of shapes other than that shown, for example right circular cylindrical shells.

I claim:

1. A centrifuge rotor comprising a hollow body and an end plate, said end plate comprising a frame fixed to the end of the body and having substantially the same expansion as the body under centrifugal stress and a closure element in the form of a thin diaphragm fixed to the frame, wherein said hollow body comprises an outer shell, a central hub and a plurality of spokes connecting said outer shell to said central hub and wherein said frame comprises an outer rim, a central hub portion and a plurality of spokes connecting said outer rim to said hub portion.

2. A centrifuge rotor comprising a hollow body including an end face and an end closure structure for the said hollow body comprising at least one frame member fixed to the end face of the body, said body and frame member having the same general shape as viewed in cross section in the direction perpendicular to the axis of the rotor,

said frame member and body also being composed of 5 materials which in relation to the shape thereof have substantially the same expansion under centrifugal stress and a diaphragm that is thin in relation to the thickness of the frame member fixed to the frame member.

3. A centrifuge rotor as claimed in claim 2, and said 10 5. A centrifuge rotor as claimed in claim 2, in which said frame member has opposite planar faces extending perpendicular to the axis of the rotor, said diaphragm being of substantially uniform thickness and fixed to one of said faces in abutting relationship therewith.

References Cited by the Examiner UNITED STATES PATENTS 433,142 7/90 Peck 233--27 1,772,573 8/30 Jones 23346 3,007,629 11/61 Boyland 23321 M. CARY NELSON, Primary Examiner.

5 JAMES L. BREWRINK, SAMUEL BOYD, Examiners 

1. A CENTRIFUGE ROTOR COMPRISING A HOLLOW BODY AND AN END PLATE, SAID END PLATE COMPRISING A FRAME FIXED TO THE END OF THE BODY AND HAVING SUBSTANTIALLY THE SAME EXPANSION AS THE BODY UNDER CENTRIFUGAL STRESS AND A CLOSURE ELEMENT IN THE FORM OF A THIN DIAPHRAGM FIXED TO THE FRAME, WHEREIN SAID HOLLOW BODY COMPRISES AN OUTER SHELL, A CENTRAL HUB AND A PLURALITY OF SPOKES CONNECTING SAID OUTER SHELL TO SAID CENTRAL HUB AND WHEREIN SAID FRAME COMPRISES AN OUTER RIM, A CENTRAL HUB PORTION AND A PLU- 